# What is pH

pH is a measure of the hydorgen ion concentration of a solution. Solutions with a high concentration of hydrogen ions have a low pH and solutions with a low concentrations of H+ ions have a high pH. This may seem like a confusion way to express these reationships, and it is, until you understand what pH stands for. The equation that defines pH is given as follows:

pH=-log[H+] concentration,

the pH is equal to minus the log of the H+ concentration.

For example is the H+ concentration is very low, lets say about 0.0000001M, then the pH is

pH= -log[.0000001] whis is the same as -log[1 X 10-7]

the term log[1 X 10-7] = -7

- (-7) = 7

Look at the following table

# hydrogen ion concetration  pH  solutions with a pH of  .1M  1    .01M  2  coke and orange juice  .001  3    .0001  4    .00001  5  black coffee  .000001  6    .0000001  7  pure water  .00000001  8    .000000001  9  baking soda  .0000000001  10    .00000000001  11    .000000000001  12  household bleach  .0000000000001  13  oven cleaner

From this table you will notice a few relationships

• a difference of one pH unit (ie from pH 2 to pH 3) is a ten fold (10X) difference in H+ ion concentration.

• pure water should have a pH of 7.0

• solutions with a pH below 7.0 are termed acidic and solutions with a pH above 7.0 are termed basic.